EXAMPLE 13 The Solar System

The American moon landings in 1969 and later, as well as all other space missions, were possible because of the predictability, or determinism, of the solar system. The moon and planets follow their orbits like clockwork. So how could the solar system be chaotic?

Over tens of millions of years, the orbit of each planet is chaotic, meaning that the slightest change in its position or velocity—due to, say, a comet passing nearby—could produce a huge difference later. In mid-2015, we learned that at least two of Pluto’s five moons (Nix and Hydra, discovered only in 2005) rotate and tumble chaotically.